Oil and gas development that is done with hydraulic fracturing (commonly known as fracking) requires significant amounts of water. Hydraulic fracturing is an oil and natural gas production technique that involves the injection of millions of gallons of water, plus chemicals and sand, underground at very high pressure in order to create fractures in the underlying geologic formations to allow natural gas to escape. The sand is used to keep the fractures open and allow oil or gas to flow more efficiently. Hydraulic fracturing is commonly used in many types of geologic formations such as coal beds, shale plays, and previously drilled wells to further stimulate production. Shale gas is found in shale “plays,” which are shale formations containing significant accumulations of natural gas and which share similar geologic and geographic properties.
FIG. 1 is an illustration of the site of a fracking operation. A hole is drilled in the ground into which a casing is laid. Fracking fluid is pumped under pressure into the casing and down through the earth into a gas/oil-bearing formation below. The fracking fluid opens hydraulic fractures that are held open by the sand. Oil or gas trapped in the gas/oil-bearing formation traverses the hydraulic fractures and is extracted up through the casing. In addition, wastewater exits the casing at the surface and is collected in wastewater ponds near the hole.
Thirty-three states have oil and/or natural gas production and, according to the Interstate Oil and Gas Compact Commission, more than 90% of U.S. oil and natural gas wells use hydraulic fracturing. Tens of thousands—if not hundreds of thousands—more wells are planned across the country over the next decade. Hundreds of different types of chemicals are used in fracking operations. In some cases, hydraulic fracturing fluids can contain a variety of substances, such as diesel fuel, acids, and acetone. These substances make it difficult to dispose of the very large amounts of water used in fracking. While only a small fraction of the fluid volume used in any fracturing operation consists of undesirable substances, the volume of fluids needed for each “frack job” is so great, sometimes millions of gallons, that a relatively small amount of contaminant can cause a major problem in the disposal of the wastewater. Furthermore, water continues to be a precious resource on its own. Therefore, it is of value to clean and recover as much of the water as possible. The water that is recovered could then be used for further fracking jobs, returned to local waterways, such as streams and rivers, etc., or used for other purposes.
Cleaning up the wastewater from a fracking site can be an expensive and difficult task. Therefore, there is a significant need for a method and apparatus that can be used to clean up dirty wastewater from uses like fracking that produce relatively large quantities of contaminated wastewater. The term “dirty water” is used through this disclosure to refer generally to any aqueous solution that comprises elements that would be desirable to have removed from the H2O in which those elements are suspended, dissolved, or otherwise combined.
As a separate matter, it should be noted that alumina is used in a wide spectrum of non-metallurgical applications. These include: (1) manufacturing of ceramics, (2) to adsorb gases; (3) as a catalysis; and (4) as an active substance carrying agent, etc. The principle way alumina is produced today is by a method called the “Bayer process”. The Bayer process is the principal industrial means of refining bauxite to produce alumina (aluminium oxide). Bauxite is the most important ore of aluminium. It contains only 30-60% aluminium oxide (Al2O3). The rest of the material is a mixture of silica, various iron oxides, and titanium dioxide. In the Bayer process, bauxite ore is heated in a pressure vessel along with a sodium hydroxide solution (caustic soda) at a temperature of 150° C. to 200° C. At these temperatures, the aluminium is dissolved as sodium aluminate in an extraction process. After separation of the residue by filtering, aluminium hydroxide is precipitated when the liquid is cooled and then seeded with fine-grained aluminum hydroxide.
However, in many cases, the Bayer-produced alumina does not meet the increasingly high requirements imposed for use of alumina in many current applications. Some of these requirements include: (1) having an advanced surface, (2) having a high level of chemical purity, and (3) having a relatively high level of phase homogeneity. In some such cases, the desired physical and chemical properties are achieved by additional steps, such as mechanical milling, application of a “sol-gel technique”, use of chemical vapor deposition, controlling the atmosphere calcination and other techniques. The necessity of each step depends on the particular requirements for the desired alumina properties. In order to provide a more efficient process, a method of advanced materials production referred to as hydrothermal processing has come to the attention of some people. The term hydrothermal processing covers the broad spectrum of different techniques. It commonly implies the use of aqueous solutions at elevated temperatures (>100° C.) and pressures (>0.1 MPa).
While hydrothermal processing includes the extraction of pure Al(OH)3 as performed by the Bayer process, newer hydrothermal techniques tend to use higher temperatures and pressures (in near-critical or supercritical field) than that of the Bayer process (200° C., 3 MPa). However, the success of such advanced materials production techniques used under hydrothermal conditions is usually bound up with unique properties, such as the density, viscosity, ionic product, dielectric constant, etc. of water at high temperature and pressure. While the changes that occur in the properties of water over temperature and pressure are well known, the role of water and the mechanism of chemical reactions under hydrothermal conditions are not always clear. The particular role of water and the particular mechanism in play can change depending on the particular reaction and reaction conditions.
In addition, the cost of producing aluminum hydroxide through the hydrothermal process can make it impractical or uneconomical to do so. Even in cases in which the market can support production of aluminum hydroxide through the hydrothermal process, the cost of the resulting aluminum hydroxide can be high. Therefore, it would be desirable to provide a means by which pure aluminum hydroxide may be produced at a lower cost.
The presently disclosed method and apparatus provides an efficient and cost effect method and apparatus for both cleaning contaminated wastewater and producing economical and useful aluminum hydroxide (and other useful byproducts) in an environmentally clean and efficient way that is beneficial to the environment.